In telecommunication networks such as those based on the 3rd Generation Partnership Project (3GPP) specifications, to facilitate uplink (UL) communication from a terminal device (which is also called as a user device or user equipment) to a network device (which is also called as a base station), the network device may schedule, upon request, UL resource such as a UL subframe in a UL grant to the terminal device using a control channel. The terminal device may send UL data in that scheduled subframe. Depending on whether the uplink data is successfully received, the network device may transmit an acknowledgement/non-acknowledgement (ACK/NACK) feedback so that the terminal device may determine whether to retransmit the UL data or not.
In some advanced services such as mobile broadband service (MBB), there is certain delay tolerance for the terminal device to obtain the ACK/NACK feedback after the transmission of the UL data. It has therefore been proposed in some new access (NX) or license assisted access (LAA) concept reports to aggregate and schedule a plurality of consecutive subframes in one UL grant. The multiple-subframe scheduling is especially suitable for new radio access techniques (NR). According to some legacy techniques, the number of subframes to be scheduled in one transmission opportunity (TXOP) (for example, 6 ms or 8 ms) is small due to the transmission time interval (TTI) length (1 ms) and the grant delay (the time from the UL grant transmission to the UL data transmission is 4 ms). For NR, the TTI length and the grant delay is much smaller (0.125 ms of TTI and much shorter grant delay) while the TXOP duration remains the same. Therefore, the number of contiguous subframes that can be scheduled in one TXOP via a UL grant is large.
According to multiple-subframe scheduling, the network device schedules a plurality of subframes in one UL grant to the terminal device using a single control channel. An ACK/NACK feedback message of correct/incorrect reception is provided for the aggregation of subframes instead of the individual subframes. This reduces both control and feedback signaling overhead. Typically, the network device decides the number of subframes to be scheduled to the terminal device based on a buffer status report (BSR) from the terminal device. The number of scheduled subframes matches exactly the buffer status reported by the terminal device. Upon receiving the scheduled subframes, the terminal device may transmit all the buffered data in just the granted subframe resources.
In use cases with uncertain channel availability, the terminal device detects whether a subframe is idle or busy before it starts a transmission in this subframe, which is called as a listen-before-talk (LBT) process. Such uncertain channel availability may occur for various reasons, one of which is the unlicensed operations. Since it is difficult for the network device to take the uncertain channel availability into account when scheduling the subframes, some of the scheduled subframes may be found to be busy though the LBT process after the grant is received. In this case, the terminal device may fail to transmit all the buffered UL data in current scheduled subframes. As a result, a new request for subframe scheduling is needed, which increases the signaling overhead and data transmission delay.